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Cracking and plastic wrap.

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Forum topic by Novum posted 01-26-2022 10:23 PM 541 views 0 times favorited 8 replies Add to Favorites Watch
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Novum

18 posts in 149 days


01-26-2022 10:23 PM

I am sure this has been covered many times…but as a newbie to this site I don’t know how to search archives.

Anyway…turned the outside of a small green wood hickory bowl two days ago. Today when I went to start on the inside the whole thing was cracked. Didn’t take much to split it I have with a hammer and chisel

For future reference, if I turn the outside and wait to do the inside should I wrap it in plastic until am ready to start the inside? Would that avoid the issue?

Bigger question: how to avoid cracking.

Thanks..world of help here!


8 replies so far

View Axis39's profile

Axis39

621 posts in 1055 days


#1 posted 01-27-2022 02:53 PM

There’s a guy on Youtube… Look for ‘Turn a wood bowl’ I think… Anyway, he has several videos on turning green wood bowls.

I am rather new to turning, so I don’t have a solid opinion yet. However, that’s never stopped me form spouting off on the Interwebs before!

Mostly, you have to slow down the drying process…. Waiting a day in between was probably a mistake. Should probably turn inside and outside at one sitting, then follow some of the standard practices. Might think about getting a finish on it right away, or turning it bigger, letting it dry and then turning it again?

-- John F. SoCal transplant, chewer uppper of good wood

View PCDub's profile

PCDub

397 posts in 1702 days


#2 posted 01-27-2022 03:05 PM

Turn it down to near your final shape, then store it in a paper bag or box surrounded by wood shavings and leave it for a month or two. It will slow the drying down, and though it may be warped from what you thought you had, you’ll have enough wood left to complete it without cracking.

I have no experience with hickory, but others may be able to say if there are special considerations for it.

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Novum

18 posts in 149 days


#3 posted 01-27-2022 03:28 PM

Knowing me, at some point later I would find this box of shavings and burn it not knowing I had stored something in it.

At this stage all projects are experiments. Many different opinions out there on stuff such as, carbide? HSS? 100% Tung oil or formby’s, wax no wax, what kind of wax, abrasive polish or not? Mortise or tenon? Wrap in cling wrap or plastic bag or shavings? 80 grit or 100 grit grinding wheel.

The easy part is getting the wood. My goal is to only use wood i harvest from my property… apple, cedar, hickory, will try oak and pine….not sure I want to try locust, Maybe sycamore.

View Lazyman's profile

Lazyman

9591 posts in 2845 days


#4 posted 01-27-2022 03:29 PM

Turning the outside and waiting to do the inside will have very little affect, IMO. I approach this by doing an initial rough turning, inside and out, to a thickness that is about 10% the rough width of the bowl—a 10” wide bowl would would have 1” thickness. Next takes patience. I scoop up enough of the wet shavings from the bowl and bury the bowl in them in a paper bag to slow down the drying rate. This allows the wood to dry more evenly and reduces warping and cracking but may not completely eliminate it. Note that this can take anywhere from 6 weeks to 6 months depending upon just how wet it is, the humidity, the type of wood and the ring and grain orientation of the initial blank. Also note that it is a good idea to sort of fluff the shavings every week or so for the first few weeks to prevent mildew from growing on your bowl.

When I do stop before completing the rough turning, even just to take a break for lunch for example, I will put a plastic bag or something to slow down the drying during the break so that I don’t come back to a cracked blank. In extreme cases, when hollowing a vase for example where it can take a while, I will even spray the blank with water to make sure that it stays wet until I have time to bury it in the shavings.

If I have a blank that I do not think is going to crack much, I will sometimes use my microwave to speed up the drying process by heating it at 30-50% power setting for 2-3 minutes at a time repeatedly over the course of several hours, letting it completely cool between cycles. I record the weight using a kitchen scale before each heating cycle and when it stops losing weight I know that it is dry enough to proceed. I will usually wait over night and do one more cycle to make sure that it has actually stopped losing weight.

An important way to prevent this cracking during drying is to insure that there are no center rings, sometimes called pith, in your blank. The first 5-10 years of growth are what is known as juvenile wood. Juvenile wood usually contracts much more quickly when drying than the later growth and is responsible for most of the serious cracking that occurs. If you can eliminate these first years of growth either before or during turning, you will significantly reduce both warping and cracking as the rough turned bowl drys.

EDIT to Add: I forgot to mention that I will write the rough turn date and weight (and sometimes species of wood) on the bottom of the rough bowl before I put it in the shavings to dry. I will periodically weigh it and write the weight on the bowl along with that date so that I can tell when it is dry enough. When it seems to have stopped losing weight, I sometimes will try some short microwave cycles to see if it will still lose weight before proceeding.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View TheDane's profile

TheDane

6056 posts in 5121 days


#5 posted 01-27-2022 05:16 PM

Rough turning and drying in a bag as detailed above is a very good way to reduce cracking, but there is one additional step that may help … round over the edges (inside and outside) of the rim. Cracks are more likely to occur on a sharp (e.g. 90-degree) edge than a rounded edge.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View Novum's profile

Novum

18 posts in 149 days


#6 posted 01-27-2022 05:58 PM

All great tips. Thanks!

View LesB's profile

LesB

3470 posts in 4901 days


#7 posted 01-27-2022 06:32 PM

+! for Lazyman’s info. It is always best on wet wood to try to rough out the inside and outside at the same time with no break to balance the stress as the wood starts to dry. Even on pieces I thought were completely dry I have had cracks develop if I only turned one side and left it for any period of time before completing it.

The microwave method speeds things up a lot. I like to use the brown paper bag method to trap some of the moisture in the bag which reduces the stress between the inner wood and surface….It is like a steam kiln.

Additionally during the drying process I check frequently and if I see small cracks forming I use medium CA glue on them and most of the time this will stop them from getting larger. It is also good for filling in small cracks that do form and adding fine sawdust and CA glue in larger cracks makes a good filler.

-- Les B, Oregon

View OSU55's profile

OSU55

3037 posts in 3447 days


#8 posted 01-27-2022 08:42 PM

When turning wet wood, and most thick blanks, even ones purchased with wax coating that have been in your shop for years, are still wet. If they arent cracked, its damp in the center.

Not surprised it cracked. Wet in-process work needs covered when you arent cutting, even a 5 min break. I wrap a plastic trash bag around mine, lathe mounted. If its going to a few days before I get back to I pull it off the chuck and put it in a plastic trash bag. Kept them this way for a few weeks without mold. Since you are new and may take a while to cut a project, keep a spray bottle of water around and sprits a little on the blank every 15 min or so to keep it wet. Most times after finishing the OD of bowls and hollow forms I wrap stretch packing wrap around the OD so the piece doesnt dry out too much.

Yep, lots of opinions on tools, accessories, finishes – just gotta be smart enough to sort through the BS (there’s a lot of it) and find what works. Join the AAW and a chapter near you, that can help a lot.
Drying finished pieces – several ways to do it. In a hurry use a microwave. I use heavy kraft paper (grocery) bags, doubled if fairly wet, bag it, weigh it, write on the bag. Double bagging works better than shavings, and less mess. Reuse bags many times. After a few weeks weight again write it on the bag. Weigh every few days, when it stops losing weight its reached equilibrium, dry as it will get where you put it. Ready to sand and finish. For twice turned bowls, good rule of thumb is leave 10% wall thickness when roughed out, 10” bowl 1” wall. Provides enough material to turn round after warping while drying.

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